There are economic and clinical incentives for both patients and physicians to preferentially utilize generic medications when available, since switching to generic prescription drugs can reduce total prescription medication expenditures due to their substantially lower costs. The Congressional Budget Office estimates that generic substitution under Medicare Part D reduced total prescription drug costs for Medicare beneficiaries in 2007 by $33 billion, 55% lower than if no generic substitution had occurred. The Abbreviated New Drug Application (ANDA) usually includes in vivo plasma bioequivalence studies to demonstrate therapeutic equivalence of test product to the reference product. This method has been time-tested, through retrospective studies and in clinical practice, as an effective method to ensure comparable safety and efficacy of the test product. However, there are situations where in vivo plasma bioequivalence studies may not be the appropriate route to generic approval. The need to provide access to new, safe and effective generic drugs for patients is therefore met with controversial innovative evaluation methods. It is important for the FDA to monitor the post-approval drug safety, effectiveness, usage, and substitution patterns of these generic drugs. We propose the following specific aims: 1) Assess clinical outcomes with brand and generic drugs by conducting a systematic evaluation of clinical trials and observational studies; 2) Estimate generic and brand medication utilization and switchback rates and medical service utilization associated with generic switching using Medicare claim databases to assess individual level use of a brand product and its generics; and 3) Determine if controversy around a generic drug approval impacted perceptions of the generic drug quality by conducting a national survey of patient and physician experiences about the model brand and generic drug product use. Findings will have significant clinical and policy impacts on current and future generic drug use in the United States, as the study will inform the agency on the development of methods to assess the safety and effectiveness of generic drugs in the marketplace, especially when a controversy exists in the generic approval process. The proposed study is innovative with its proactive, mixed-methods approaches, and use of social media such as Facebook and online physician forums to conduct surveys. The expected outcomes of this study are new decision science and strategies for the Office of Generic Drugs on methods to assess the safety and effectiveness of generic drugs in the marketplace, especially when novel bioequivalence methodology has been used in the generic approval process.